Field of the Invention
The present invention relates to a fuel cell membrane electrode assembly (MEA) having a protection member for different sizes of components of the MEA (stepped MEA).
Description of the Related Art
In general, a solid polymer electrolyte fuel cell employs a solid polymer electrolyte membrane. The solid polymer electrolyte membrane is a polymer ion exchange membrane. The fuel cell includes a membrane electrode assembly (MEA) where an anode is provided on one side of the solid polymer electrolyte membrane, and a cathode is provided on the other side of the solid polymer electrolyte membrane. Each of the anode and the cathode includes a catalyst layer (electrode catalyst layer) and a gas diffusion layer (porous carbon).
In the fuel cell, the membrane electrode assembly is sandwiched between separators (bipolar plates). A predetermined number of the fuel cells are stacked together to form a fuel cell stack. For example, the fuel cell stack is mounted in a fuel cell electric vehicle as an in-vehicle fuel cell stack.
In some cases, the membrane electrode assembly has structure where components of the MEA have different sizes, i.e., the surface size of one of diffusion layers is smaller than the surface size of the solid polymer electrolyte membrane, and the surface size of the other of the gas diffusion layers is the same as the surface size of the solid polymer electrolyte membrane (stepped MEA). In this regard, reduction in the thickness of the solid polymer electrolyte membrane is attempted to reduce the amount of relatively expensive material used for the solid polymer electrolyte membrane. Therefore, in order to protect the thin solid polymer electrolyte membrane having insufficient strength, as a protection member, for example, a frame equipped MEA including a resin frame member is adopted.
As the frame equipped MEA, for example a membrane electrode assembly disclosed in Japanese Laid-Open Patent Publication No. 2007-066766 (hereinafter referred to as conventional technique 1) is known. In the membrane electrode assembly, as shown in FIG. 17, an anode catalyst layer 2a and an anode diffusion layer 2b are provided on one side of a membrane 1, and a cathode catalyst layer 3a and a cathode diffusion layer 3b are provided on the other side of the membrane 1 to form an MEA 4 having different sizes of components (stepped MEA).
The surface area of the anode diffusion layer 2b is larger than the surface area of the cathode diffusion layer 3b. The outer end of the membrane 1 where the cathode diffusion layer 3b is provided is joined to a gasket structure body 5 through an adhesive layer 6.